Kawaski Fb460v(fires But Won't Start)

I just bought an old Dixon ZTR427Riding Lawn Mower. It has a Kawasaki FB460v engine. It started and ran fine for a few minutes, then belt came off & it died. Fixed the belt , but it doesn't start now. It's firing but it will not start. have bought a new battery(old one was bad) got new spark plug.
If anyone has any experience with this engine or information that would help me . I would greatly appreciate your help.